A man found with fatal stab wounds in the communal hallway of his home was named by police today.
Gordon Stalker, 51, was discovered unconscious when police and ambulance workers were called to an address in Elm Grove, Brighton, East Sussex, just after 10am on Monday.
Despite efforts to revive him, he died shortly afterwards.
Sussex Police believe he was the subject of a targeted attack and knew his killer.
A post-mortem examination carried out yesterday confirmed his death was caused by a number of stab wounds to the chest and side of his body.
Detective Chief Inspector Trevor Bowles, who is leading the major crime branch investigation into the incident, said officers "urgently" needed to trace the murder weapon used, believed to be a knife.
He also appealed to anyone who may have noticed an altercation outside the terraced property, which is understood to be made up of individual rented rooms, to come forward.
Mr Bowles said: "We still urgently need to trace the murder weapon. I believe that a knife has been used to commit this murder.
"Should anyone find a blood-stained knife, please call us. It is vital that we trace this weapon.
"Specialist police search officers have been searching the area for a weapon and today drains are also being checked.
"We have spoken to some witnesses who are helping to put together exactly what happened and why. But I still urge anyone who saw a confrontation on the doorstep of 67 Elm Grove at about 10am on Monday morning to come forward and help us find the killer.
"It is quite likely that the confrontation was visible to passers-by who may not have realised its seriousness."
He added: "From all the circumstances, I believe this was a targeted attack and that the victim would have known his killer."
Police cordoned off a section of Elm Grove surrounding the property, which is in a popular student area of the city, along with a cluster of nearby recycling bins.
One man was arrested at the scene on Monday and a second man was held later in Worthing, West Sussex, both on suspicion of murder.
Both have since been released without charge, although one of them is being treated as a "significant witness" to the incident.
Anyone with information about the incident is asked to contact Sussex Police quoting Operation Odessa, or Crimestoppers, anonymously, on 0800 555 111.